During the processing of a substrate in the plasma processing chamber, satisfactory results often require tight control of the process parameters. This is particularly true for processes such as deposition, etching, cleaning, etc., that are employed to manufacture modern high density integrated circuits. When the processing parameters (such as bias voltage, RF power, ion flux, plasma density, pressure, etc.) exceed a narrow, pre-defined window, a process excursion is said to have occurred. These process excursions represent undesirable events that often lead to undesirable processing results (e.g., poor etch profile, low selectivity, etc.). Accordingly, the detection, characterization, and avoidance of process excursions are important tasks for process engineers in the manufacture of integrated circuits.
Detecting process excursions is often performed via monitoring of various process parameters. Some process parameters (such as bias voltage, reflected power, etc.) may be measured directly while others may be inferred from measured parameters.
During a plasma process, such as a plasma etch process for example, polymer deposition often occurs. This polymer deposition results in a layer of film deposited on component surfaces in the chamber. The deposited film affects subsequent etch processes, increases the possibility of particulate contamination, and necessitates frequent chamber cleaning. Further, if a sufficiently thick deposition layer is present in the chamber, the sensor head may be covered with polymer, resulting in erroneous values for the sensor signal. In other processes, the film deposition may be intentional yet would affect sensor reading the same way.
Accordingly, the characterization of the deposited film on the chamber surface is desirable for the purpose of tool control, diagnostic and/or recipe adjustment in order to improve process results and process yield, as well as to avoid damage to the substrate and/or the chamber components.